The hydroformylation reaction, also known as the Oxo Reaction or Oxo Process, consists in reacting a synthesis gas made up of a mixture of carbon monoxide and hydrogen and at least one CnH2n olefin so as to obtain a mixture of aldehydes and primary alcohols containing n+1 carbon atoms. The reaction is generally catalyzed with carbonyls of transition metals such as cobalt. This type of reaction is described in detail in patents too numerous to recite. It is commercially highly important, producing products that find uses in plastics, soaps, lubricants, and other products.
The reactors in which the Oxo Process is carried out can be identical or different in all process stages. Examples of types of reactor which can be used are bubble columns, loop reactors, jet nozzle reactors, stirred reactors and tube reactors, some of which can be cascaded and/or provided with internals.
As part of the reactor of the “loop” type the liquid phase is recycled and the gas phase is allowed to exit the reactor at the top of the loop. External loop reactors are illustrated, for instance, in U.S. Pat. No. 4,312,837 (Papp et al.). The typical reactor used in Oxo is an external loop reactor, but internal loop reactors are also used.
An example of an conventional internal loop reactor is illustrated in FIG. 1 of the present disclosure. Such a reactor is made up of at least two concentric vertical tubes 1 and 2 connected to each other at their upper and lower ends. As shown in FIG. 1, the vertical column 1 of loop reactor 4 acts as the ascending branch (“riser”) while vertical column 2 acts as the descending branch (“downcomer”). The vertical columns are supplied with jacketed cooling means 3. Ascending vertical column 1 is continuously supplied at its base with the synthesis gas and liquid phase through inlet 5. Essentially all the synthesis gas and the excess liquid phase is evacuated at the upper connection 6, while essentially only the liquid phase circulates between ascending column 1 and descending column 2, said circulation illustrated by arrows 7. The difference between the specific gravities of the gas/liquid phase mixture on the one hand and the liquid phase alone on the other hand results in a difference in hydrostatic pressure between the ascending branch and the descending branch, thus leading to circulation of the liquid phase in the reactor.
Loop reactors of both the internal and external type are used in reactions other than the Oxo Process. They are useful particularly in exothermic and/or heterogenous (gas/liquid) reactions and have been used for such diverse reactions as the oxidation of p-xylene (U.S. Pat. No. 4,342,876), biotechnological reactions (WO 8804317), and the purification of water (U.S. Pat. No. 6,544,421). It is known that by varying the geometries of the reactor, it is possible to eliminate certain problems encountered in specific reactions. See, for instance, U.S. Pat. No. 4,312,837 (FR 2430794 A1); U.S. Pat. Nos. 4,342,876; 5,277,878; 5,503,810; and 6,106,789. There is, however, no shortage of problems to be solved in these systems and typically solving one problem by simply varying geometries introduces at least one new problem.
One of the main problems with conventional loop reactors, is that they are limited in size. At least in part this is simply a matter of the practical difficulty in bending large tubes. In addition, construction of large reactors is also made difficult because the vessels must be erected in the field by sliding internals, which must be standing vertically; otherwise, with reactor on its side, the internals will bend and warp. Furthermore, in the case of the Oxo Process, the reaction typically occurs at very high pressures, such as 4,000 lbs/in (or about 28 MPa), which further limits the size of the vessels as they are known to be constructed in the prior art. As far as the present inventors are aware, the largest known loop reactors have a volume of about 8-12 cubic meters.
The present inventors have discovered that by building an internal loop reactor so that the separation between the riser and downcomer portions comprises a heat exchanger, preferably one or more cooling tubes, allows for all the necessary parts to be attached to a reactor head. This allows more convenient construction of the reactor in the field and furthermore reactor volume can be increased considerably over prior art Oxo Reactors.